This episode details an experiment conducted by the ATLAS Collaboration using Large Hadron Collider data from 2015-2018. The research investigates the CP properties of the Higgs boson in its vector-boson fusion production mode, specifically focusing on its decay into two tau leptons. Utilising the Optimal Observable method and an effective field theory framework, the study aims to detect CP-violating interactions between the Higgs boson and electroweak gauge bosons. While no deviations from the Standard Model (which predicts a CP-even Higgs boson) were observed, the analysis provides stringent limits on strength parameters that describe potential beyond-Standard Model physics. The paper compares these findings with previous ATLAS and CMS Collaboration results, contributing to the ongoing effort to understand the fundamental nature of the Higgs boson.

Link to arxiv: https://arxiv.org/abs/2506.19395